Lubricating oil composition

ABSTRACT

A lubricating oil composition with enhanced deposit control capability is disclosed for engines operating under sustained high load conditions, such as natural gas engines and low-speed or medium-speed diesel engines. The composition comprises (a) a first base oil component selected from a Group I base stock, a Group II base stock, a Group III base stock, or a combination thereof, each having a kinematic viscosity at 100° C. of from 8.5 to 15 mm2/s; and (b) a second base oil component selected from a Group I base stock, a Group II base stock, a Group III base stock, or a combination thereof, each having a kinematic viscosity at 100° C. of from 4.0 to less than 8.5 mm2/s; wherein the weight ratio of the first base oil component to the second base oil component is in a range of from 1:10 to 1:1.15.

TECHNICAL FIELD

The present disclosure relates to lubricants for use in engines operatedunder sustained high load conditions, such as natural gas-fueled enginesand low-speed or medium-speed diesel-fueled engines, and to methods forenhancing the deposit control capacity of the lubricants used in suchengines, particularly those equipped with steel pistons.

BACKGROUND

It is known that internal combustion engines place enormous stresses onthe lubricating oils. The oil is required to provide good lubricationunder all conditions, provide protection against wear and corrosion, bestable to sustained levels of contamination, keep engine surfacesrelatively clean, resist thermal and/or oxidative breakdown and carryaway excess heat from the engine.

While all engines place such stresses on these lubricating oils,stationary diesel-fueled and stationary natural gas-fueled engines areparticularly challenging to the lubricating oil. For engines thatroutinely run continuously, near full load conditions, for many days orweeks, as in the case of stationary natural gas-fueled engines, and inremote locations, the demands placed on the oils used in such enginesare of a sustained rather than transient nature, often with little or nomonitoring and little or no opportunity to respond quickly to engineupsets or oil failure. This is further aggravated by the trend to higherloads and longer oil drain periods.

Original equipment manufacturers (OEMs) in recent years have beendesigning internal combustion engines in ways to provide greater powerdensity, that is, higher power produced per unit of displacement. Arecent development in engine design has been to replace aluminum pistonswith steel pistons to maintain the strength of pistons while operatingat higher pressures and temperatures.

Steel piston engines operating at high Brake Mean Effective Pressure(i.e., BMEP>20 bar) have shown a propensity to form excessive depositson mechanical components (e.g., pistons, piston rings, cylinder liners,etc.) leading to shorter componentry life when lubricated withconventional lubricant additive packages formulated with the highestviscosity cut of API group base oil (e.g., a heavy neutral base oil) toachieve the oil life characteristics desired.

It has now been surprisingly found that partial substitution of theheavy neutral base oil with lighter neutral base stocks provides alubricating oil composition which exhibits improved resistance todeposit formation in engines, particularly steel piston engines,operating under sustained high load conditions.

SUMMARY

In one aspect, there is provided a natural gas engine lubricating oilcomposition comprising: (a) a first base oil component selected from aGroup I base stock, a Group II base stock, a Group III base stock, or acombination thereof, each having a kinematic viscosity at 100° C. offrom 8.5 to 15 mm²/s; and (b) a second base oil component selected froma Group I base stock, a Group II base stock, a Group III base stock, ora combination thereof, each having a kinematic viscosity at 100° C. offrom 4.0 to less than 8.5 mm²/s; wherein the weight ratio of the firstbase oil component to the second base oil component is in a range offrom 1:10 to 1:1.15.

In another aspect, there is provided a low-speed or medium-speed dieselengine lubricating oil composition comprising: (a) a first base oilcomponent selected from a Group I base stock, a Group II base stock, aGroup III base stock, or a combination thereof, each having a kinematicviscosity at 100° C. of from 8.5 to 15 mm²/s; and (b) a second base oilcomponent selected from a Group I base stock, a Group II base stock, aGroup III base stock, or a combination thereof, each having a kinematicviscosity at 100° C. of from 4.0 to less than 8.5 mm²/s; wherein theweight ratio of the first base oil component to the second base oilcomponent is in a range of from 1:10 to 1:1.15.

In another aspect, there is provided a method of controlling depositformation in an internal combustion engine selected from a natural gasengine, a low-speed diesel engine or a medium-speed diesel engine whichcomprises operating the internal combustion engine with the lubricatingoil composition disclosed herein.

In yet another aspect, there is provided the use of the lubricating oilcomposition described herein for the purpose of controlling depositformation in an internal combustion engine selected from a natural gasengine, a low-speed diesel engine or a medium-speed diesel engine.

DETAILED DESCRIPTION

Terms

A “major amount” means 50 wt. % or more of a composition.

A “minor amount” means less than 50 wt. % of a composition.

As employed herein, the terms “base stock” and “base oil” are usedsynonymously and interchangeably.

A “dual-fuel engine” refers to an engine that can run on a mixture ofnatural gas and diesel. The combination of natural gas and diesel maycomprise at least 60% natural gas.

All percentages reported are weight % on an active ingredient basis(i.e., without regard to carrier or diluent oil) unless otherwisestated.

All ASTM standards referred to herein are the most current versions asof the filing date of the present application.

INDUSTRIAL APPLICABILITY

The lubricating oil composition disclosed herein is utilized in anatural gas engine, a low-speed diesel engine or a medium-speed dieselengine. The engine may be a two-stroke engine, three-stroke engine,four-stroke engine, five-stroke engine, or six-stroke engine. The enginemay also include any number of combustion chambers, pistons, andassociated cylinders (e.g., 1-24). For example, in certain embodiments,the engine may be a large-scale industrial reciprocating engine having2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 16, 18, 20, 24 or more pistonsreciprocating in cylinders. In certain embodiments, the piston may be analuminum piston or a steel piston (e.g., steel or any of a variety ofsteel alloys, such as 42CrMo4V or 38MnVS6).

The natural gas engine may be a stationary natural gas engine, astationary biogas engine, a stationary landfill gas engine, a stationaryunconventional natural gas engine, or a dual-fuel engine.

Diesel engines may generally be classified as low-speed, medium-speed orhigh-speed engines. Herein, a “low-speed” diesel engine means acompression-ignition internal combustion engine that is driven at arotational speed that is less than 500 revolutions per minute (rpm),such as marine crosshead diesel engines; a “medium-speed” diesel enginemeans a compression-ignition internal combustion engine that is drivenat a rotational speed of 500 to 1800 rpm, such as locomotive dieselengines, marine trunk piston diesel engines, or land-based stationarypower diesel engines; and a “high-speed” diesel engine means acompression-ignition internal combustion engine that is driven at arotational speed that is higher than 1800 rpm, such as diesel enginesfor highway vehicles.

The lubricating oil composition disclosed herein may be utilized incontrolling deposits in engines operating under high sustained loadconditions, such as a Brake Mean Effective Pressure (BMEP) of at least20 bar (2.0 MPa), e.g., at least 22 bar (2.2 MPa), at least 24 bar (2.4MPa), at least 26 bar (2.6 MPa), 20 to 30 bar (2.0 to 3.0 MPa), 22 to 30bar (2.2 to 3.0 MPa), 22 to 28 bar (2.2 to 2.8 MPa), or 24 to 30 bar(2.4 to 3.0 MPa).

The lubricating oil composition of the present disclosure may provideadvantaged deposit control performance in any of a number of mechanicalcomponents of an engine. The mechanical component may be a piston, apiston ring, a cylinder liner, a cylinder, a cam, a tappet, a lifter, agear, a valve, a valve guide, or a bearing including a journal, aroller, a tapered, a needle, or a ball bearing. In some aspects, themechanical component comprises steel.

Base Oils

Groups I, II, III, IV and V are broad categories of base oil stocksdeveloped and defined by the American Petroleum Institute (APIPublication 1509—Appendix E) to create guidelines for lubricant baseoils. Group I base stocks contain less than 90% saturates and/or greaterthan 0.03% sulfur and have a viscosity index greater than or equal to 80and less than 120. Group II base stocks contain greater than or equal to90% saturates and less than or equal to 0.03% sulfur and have aviscosity index greater than or equal to 80 and less than 120. Group IIIbase stocks contain greater than or equal to 90% saturates and less thanor equal to 0.03% sulfur and have a viscosity index greater than orequal to 120. Group IV base stocks are polyalphaolefins. Group V basestocks include all other base stocks not included in Groups I, II, IIIor IV. Table 1 summarizes properties of each of these five groups.

TABLE 1 Base Oil Properties Group⁽¹⁾ Saturates⁽²⁾ Sulfur⁽³⁾ ViscosityIndex⁽⁴⁾ Group I <90% and/or >0.03% 80 to <120 Group II ≥90% ≤0.03% 80to <120 Group III ≥90% ≤0.03% ≥120 Group IV Polyalphaolefins (PAOs)Group V All other base stocks not included in Groups I, II, III or IV⁽¹⁾Groups I-III are mineral oil base stocks ⁽²⁾ASTM D2007 ⁽³⁾ASTM D2622,ASTM D3120, ASTM D4294 or ASTM D4927 ⁽⁴⁾ASTM D2270

The lubricating oil composition of the present disclosure is a mixtureof at least two base oil components. The mixture of the at least twobase oil components comprises a minor amount of first base oil componenthaving a kinematic viscosity at 100° C. of from 8.5 to 15.0 mm²/s (e.g.,9.0 to 14.0 mm²/s or 10.0 to 13.0 mm²/s or 10.0 to 12.0 mm²/s), whichbase oil component is selected from one or more of a Group I base stock,a Group II base stock, and a Group III base stock, in combination with amajor amount of a second base oil component having a kinematic viscosityat 100° C. of from 4.0 to less than 8.5 mm²/s (e.g. 4.5 to 8.0 mm²/s,5.0 to 8.0 mm²/s, or 5.0 to 7.5 mm²/s), which base oil component isselected from one or more of a Group I base stock, a Group II base stockand a Group III base stock. In some aspects, the first base oilcomponent may be selected from a Group II base stock, a Group III basestock, or a combination thereof. On some aspects, the second base oilcomponent may be selected from a Group II base stock, a Group III basestock, or a combination thereof.

The first base oil component of high viscosity can be made up of asingle base stock meeting the recited kinematic viscosity range or bemade up of two or more base stocks, each meeting the recited kinematicviscosity limits.

The second base oil component of low viscosity can be made up of asingle base stock meeting the recited kinematic viscosity range or itmay be made up of two or more base stocks, each of which meet therecited kinematic viscosity limit.

The weight ratio of the first base oil component to the second base oilcomponent may range from 1:10 to 1:1.15 (e.g., 1:10 to 1:6, 1:8 to 1:5,1:5 to 1:1.15, 1:6 to 1:4, 1:4 to 1:2, 1:3 to 1:1.15, 1:6 to 1:2, or 1:3to 1:1.15).

Lubricating Oil Composition

The lubricating oil composition of this disclosure can be identified byviscosity standards of the Society of Automotive Engineers (SAE) forengine oils (i.e., the SAE J300 standard). The SAE J300 viscosity gradesare summarized in Table 2.

TABLE 2 Low Shear Low Shear Low Temp. (° C.) Rate Rate High Low Temp.Pumping Kinematic Kinematic Shear Rate SAE (° C.) Cranking Viscosity⁽²⁾,Viscosity⁽³⁾ Viscosity⁽³⁾ Viscosity⁽⁴⁾, Viscosity Viscosity⁽¹⁾, mPa-sMax with (mm²/s) at (mm²/s) at (mPa-s) at Grade mPa-s Max No YieldStress 100° C. Min 100° C. Max 150° C. Min  0 W 6200 at −35 60000 at −403.8 — —  5 W 6600 at −30 60000 at −35 3.8 — — 10 W 7000 at −25 60000 at−30 4.1 — — 15 W 7000 at −20 60000 at −25 5.6 — — 20 W 9500 at −15 60000at −20 5.6 — — 25 W 13000 at −10  60000 at −15 9.3 — —  8 — — 4.0 <6.11.7 12 — — 5.0 <7.1 2.0 16 — — 6.1 <8.2 2.3 20 — — 6.9 <9.3 2.6 30 — —9.3 <12.5 2.9 40 — — 12.5 <16.3 3.5⁽⁵⁾ 40 — — 12.5 <16.3 3.7⁽⁶⁾ 50 — —16.3 <21.9 3.7 60 — — 21.9 <26.1 3.7 ⁽¹⁾ASTM D5293 ⁽²⁾ASTM D4684 ⁽³⁾ASTMD445 ⁽⁴⁾ASTM D4683, ASTM D4741, ASTM D5481 or CEC L-36-90 ⁽⁵⁾For 0 W-40,5 W-40 and 10 W-40 grades ⁽⁶⁾For 15 W-40, 20 W-40, 25 W-40 and 40 grades

The lubricating oil composition of this disclosure may be a monogradeengine oil, e.g., a SAE 20, SAE 30, SAE 40, SAE 50 or SAE 60 viscositygrade engine oil.

The lubricating oil composition of this disclosure may be a multi-gradeengine oil, e.g., an engine oil with a SAE viscosity grade of 15W-x,20W-x or 25W-x, where x may be selected from 30, 40, 50, or 60.

To obtain a finished lubricating oil composition having a desiredviscosity grade, a thickener may be added to the lubricating oilcomposition to increase its viscosity. Any suitable thickener may beused such as polyisobutylene (PIB). PIB is a commercially availablematerial from several manufacturers. Polyisobutylene is typically aviscous oil-miscible liquid having a number average molecular weight of800 to 5000 (e.g., 1000 to 2500) and a kinematic viscosity at 100° C. of200 to 5000 mm²/s (e.g., 200 to 1000 mm²/s). The amount of PIB added tothe lubricating oil composition will normally be from 1 to 20 wt. %(e.g., 2 to 15 wt. % or 4 to 12 wt. %) of the finished oil.

The lubricating oil composition may contain low levels of sulfated ash,as determined by ASTM D874. The composition may have a sulfated ashcontent of less than 1.0 wt. % (e.g., less than 0.6 wt. % or even lessthan 0.15 wt. %), based on the total weight of the composition.

In some embodiments, the lubricating oil composition may besubstantially zinc-free.

In some embodiments, the lubricating oil composition may besubstantially free of bright stock.

Additional Additives

The lubricating oil compositions of the present disclosure may containone or more performance additives that can impart or improve anydesirable property of the lubricating oil composition. Any additiveknown to those of skill in the art may be used in the lubricating oilcomposition disclosed herein. Some suitable additives have beendescribed by R. M. Mortier et al. “Chemistry and Technology ofLubricants,” 3^(rd) Edition, Springer (2010) and L. R. Rudnik “LubricantAdditives: Chemistry and Applications,” Second Edition, CRC Press(2009).

In general, the concentration of each of the additives in thelubricating oil composition, when used, may range from 0.001 to 10 wt. %(e.g., 0.01 to 5 wt. %, or 0.05 to 2.5 wt. %) of the lubricating oilcomposition. Further, the total amount of additives in the lubricatingoil composition may range from 0.001 to 20 wt. % (e.g., 0.01 to 15 wt. %or 0.1 to 10 wt. %) of the lubricating oil composition.

The present lubricating oil composition may additionally contain one ormore of the other commonly used lubricating oil performance additivesincluding antioxidants, anti-wear agent, metal detergents, dispersants,friction modifiers, corrosion inhibitors, demulsifiers, viscositymodifiers, pour point depressants, foam inhibitors, and others.

Antioxidants

Antioxidants retard the oxidative degradation of base oils duringservice. Such degradation may result in deposits on metal surfaces, thepresence of sludge, or a viscosity increase in the lubricant. Usefulantioxidants include hindered phenols, aromatic amines, and sulfurizedalkylphenols and alkali and alkaline earth metal salts thereof.

The hindered phenol antioxidant may contain a secondary butyl and/or atertiary butyl group as a sterically hindering group. The phenol groupmay be further substituted with a hydrocarbyl group and/or a bridginggroup linking to a second aromatic group. Examples of suitable hinderedphenol antioxidants include 2,6-di-tert-butylphenol,4-methyl-2,6-di-tert-butylphenol,2,2′-methylenebis(6-tert-butyl-4-methylphenol),4,4′-bis(2,6-di-tert-butylphenol) and4,4′-methylenebis(2,6-di-tert-butylphenol). The hindered phenolantioxidant may be an ester or an addition product derived from2,6-di-tert-butylphenol and an alkyl acrylate, wherein the alkyl groupmay contain from 1 to 18 carbon atoms.

Suitable aromatic amine antioxidants include diarylamines such asalkylated diphenylamines (e.g., dioctyl diphenylamine, dinonyldiphenylamine), phenyl-alpha-naphthalene and alkylatedphenyl-alpha-naphthalenes.

Anti-Wear Agents

Anti-wear agents reduce wear of metal parts. Examples of anti-wearagents include phosphorus-containing anti-wear/extreme pressure agentssuch as metal thiophosphates, phosphoric acid esters and salts thereof,phosphorus-containing carboxylic acids, esters, ethers, and amides; andphosphites. The anti-wear agent may be a zinc dialkyldithiophosphate.Non-phosphorus-containing anti-wear agents include borate esters(including borated epoxides), dithiocarbamate compounds,molybdenum-containing compounds, and sulfurized olefins.

Metal Detergents

A typical detergent is an anionic material that contains a long chainhydrophobic portion of the molecule and a smaller anionic or oleophobichydrophilic portion of the molecule. The anionic portion of thedetergent is typically derived from an organic acid such as a sulfuracid, carboxylic acid, phosphorous acid, phenol, or mixtures thereof.The counterion is typically an alkaline earth or alkali metal.

In some embodiments, the lubricating oil composition provided hereincomprises at least a neutral or overbased metal detergent as anadditive, or additive components. In certain embodiments, the metaldetergents in lubricating oil compositions acts as a neutralizer ofacidic products within the oil. In certain embodiments, the metaldetergent prevents the formation of deposits on the surface of anengine. Depending on the nature of the acid used, the detergent may haveadditional functions, for example, antioxidant properties. In certainaspects, lubricating oil compositions contain metal detergentscomprising either overbased detergents or mixtures of neutral andoverbased detergents. The term “overbased” is intended to defineadditives which contain a metal content in excess of that required bythe stoichiometry of the particular metal and the particular organicacid used. The excess metal exists in the form of particles of inorganicbase (e.g., a hydroxide or carbonate) surrounded by a sheath of metalsalt. The sheath serves to maintain the particles in dispersion in aliquid oleaginous vehicle. The amount of excess metal is commonlyexpressed as the ratio of total equivalence of excess metal toequivalence of organic acid and is typically in a range of 0.1 to 30.

Some examples of suitable metal detergents include sulfurized orunsulfurized alkyl or alkenyl phenates, alkyl or alkenyl aromaticsulfonates, borated sulfonates, sulfurized or unsulfurized metal saltsof multi-hydroxy alkyl or alkenyl aromatic compounds, alkyl or alkenylhydroxy aromatic sulfonates, sulfurized or unsulfurized alkyl or alkenylnaphthenates, metal salts of alkanoic acids, metal salts of an alkyl oralkenyl multiacid, and chemical and physical mixtures thereof. Otherexamples of suitable metal detergents include metal sulfonates,phenates, salicylates, phosphonates, thiophosphonates and combinationsthereof. The metal can be any metal suitable for making sulfonate,phenate, salicylate or phosphonate detergents. Non-limiting examples ofsuitable metals include alkali metals, alkaline metals and transitionmetals. In some embodiments, the metal is Ca, Mg, Ba, K, Na, Li or thelike. An exemplary metal detergent which may be employed in thelubricating oil compositions includes overbased calcium phenate.

Ashless Dispersants

A dispersant is an additive whose primary function is to hold solid andliquid contaminations in suspension, thereby passivating them andreducing engine deposits at the same time as reducing sludgedepositions. For example, a dispersant maintains in suspensionoil-insoluble substances that result from oxidation during use of thelubricant, thus preventing sludge flocculation and precipitation ordeposition on metal parts of the engine.

Dispersants are usually “ashless”, being non-metallic organic materialsthat form substantially no ash on combustion, in contrast tometal-containing, and hence ash-forming materials. They comprise a longhydrocarbon chain with a polar head, the polarity being derived frominclusion of at least one nitrogen, oxygen or phosphorus atom. Thehydrocarbon is an oleophilic group that confers oil-solubility, having,for example, 40 to 500 carbon atoms. Thus, ashless dispersants maycomprise an oil-soluble polymeric backbone.

A preferred class of olefin polymers is constituted by polybutylenes,specifically polyisobutylenes (PIB) or poly-n-butylenes, such as may beprepared by polymerization of a C₄ refinery stream.

Dispersants include, for example, derivatives of long chainhydrocarbon-substituted carboxylic acids, examples being derivatives ofhigh molecular weight hydrocarbyl-substituted succinic acid. Anoteworthy group of dispersants is constituted byhydrocarbon-substituted succinimides, made, for example, by reacting theabove acids (or derivatives) with a nitrogen-containing compound,advantageously a polyalkylene polyamine, such as a polyethylenepolyamine. Typical commercially available polyisobutylene-basedsuccinimide dispersants contain polyisobutylene polymers having a numberaverage molecular weight ranging from 900 to 2500, functionalized bymaleic anhydride, and derivatized with polyamines having a molecularweight of from 100 to 350.

Other suitable dispersants include succinic esters and ester-amides,Mannich bases, polyisobutylene succinic acid (PIBSA), and other relatedcomponents.

Succinic esters are formed by the condensation reaction betweenhydrocarbon-substituted succinic anhydrides and alcohols or polyols. Forexample, the condensation product of a hydrocarbon-substituted succinicanhydride and pentaerythritol is a useful dispersant.

Succinic ester-amides are formed by condensation reaction betweenhydrocarbon-substituted succinic anhydrides and alkanol amines. Forexample, suitable alkanol amines include ethoxylatedpolyalkylpolyamines, propoxylated polyalkylpolyamines andpolyalkenylpolyamines such as polyethylene polyamines. One example ispropoxylated hexamethylenediamine.

Mannich bases are made from the reaction of an alkylphenols,formaldehyde, and a polyalkylene polyamines. Molecular weights of thealkylphenol may range from 800 to 2500.

Nitrogen-containing dispersants may be post-treated by conventionalmethods to improve their properties by reaction with any of a variety ofagents. Among these are boron compounds (e.g., boric acid) and cycliccarbonates (e.g., ethylene carbonate).

Friction Modifiers

A friction modifier is any material or materials that can alter thecoefficient of friction of a surface lubricated by any lubricant orfluid containing such material(s). Friction modifiers includealkoxylated fatty amines, borated fatty epoxides, fatty phosphites,fatty epoxides, fatty amines, borated alkoxylated fatty amines, metalsalts of fatty acids, fatty acid amides, glycerol esters, boratedglycerol esters and fatty imidazolines. As used herein, the term “fatty”means a hydrocarbon chain having 10 to 22 carbon atoms, typically astraight hydrocarbon chain.

Other known friction modifiers comprise oil-soluble organo-molybdenumcompounds. Such organo-molybdenum friction modifiers also provideantioxidant and anti-wear credits to a lubricating oil composition.Suitable oil-soluble organo-molybdenum compounds have amolybdenum-sulfur core. As examples, there may be mentioneddithiocarbamates, dithiophosphates, dithiophosphinates, xanthates,thioxanthates, sulfides, and mixtures thereof. The molybdenum compoundmay be dinuclear or trinuclear.

Corrosion Inhibitors

Corrosion inhibitors protect lubricated metal surfaces against chemicalattack by water or other contaminants. Suitable corrosion inhibitorsinclude polyoxyalkylene polyols and esters thereof, polyoxyalkylenephenols, thiadiazoles and anionic alkyl sulfonic acids.

Viscosity Modifiers

Viscosity modifiers provide lubricants with high and low temperatureoperability. These additives increase the viscosity of the oilcomposition at elevated temperatures which increases film thickness,while having limited effect on viscosity at low temperatures.

Suitable viscosity improvers include high molecular weight hydrocarbons,polyesters and viscosity index improver dispersants that function asboth a viscosity index improver and a dispersant. Typical molecularweights of these polymers are in a range of 1000 to 1,000,000 (e.g.,2000 to 500,000 or 25,000 to 100,000).

Examples of suitable viscosity improvers are polymers and copolymers ofmethacrylate, butadiene, olefins, or alkylated styrenes. Polyisobutyleneis a commonly used viscosity modifier. Another suitable viscositymodifier is polymethacrylate (copolymers of various chain length alkylmethacrylates, for example), some formulations of which also serve aspour point depressants. Other suitable viscosity modifiers includecopolymers of ethylene and propylene, hydrogenated block copolymers ofstyrene and isoprene, and polyacrylates (copolymers of various chainlength acrylates, for example). Specific examples includestyrene-isoprene or styrene-butadiene based polymers of 50,000 to200,000 molecular weight.

Pour Point Depressants

Pour point depressants lower the minimum temperature at which a fluidwill flow or can be poured. Suitable pour point depressants include C₈to C₁₈ dialkyl fumarate/vinyl acetate copolymers, polyalkylmethacrylatesand the like.

Foam Inhibitors

Foam inhibitors retard the formation of stable foams. Examples ofsuitable foam inhibitors include polysiloxanes, polyacrylates, and thelike.

EXAMPLES

The following illustrative examples are intended to be non-limiting.

To determine the effect of base oil on deposit control in an engine,lubricating oil compositions were prepared having the formulations setforth in the following Examples. The compositions were prepared bymixing the base oil(s) with additive packages according to conventionalpreparation methods. Base oil properties are listed in Table 3. Depositperformance of the lubricant oil compositions was measured using thePenn State Micro-Oxidation Test after 35 minutes at 260° C. (SAETechnical Paper 801362).

TABLE 3 Base Oil Properties ASTM Property Method Base Oil 1 Base Oil 2Kinematic Viscosity, 100° C., mm²/s D445 11.46 6.58 Viscosity IndexD2270 106 105 Saturates, % D2007 97.2 97.6 Aromatics, % D2007 2.6 2.5Sulfur, wt. % D2622 0.0018 0.0008 NOACK Volatility, % D5800 1.95 10.87CCS Viscosity, −35° C., mPa-s D5293 175800 23650 CCS Viscosity, −30° C.,mPa-s D5293 69400 13100 CCS Viscosity, −25° C., mPa-s D5293 30900 6400CCS Viscosity, −20° C., mPa-s D5293 15200 3300 CCS Viscosity, −15° C.,mPa-s D5293 7500 1875 CCS Viscosity, −10° C., mPa-s D5293 4100 1205

Examples 1-2

Lubricating oil compositions 1 and 2 were formulated to meet ashlessnatural gas engine oil specifications and major natural gas enginemanufacturers' requirements. The results are presented in Table 4.

TABLE 4 Example 1 Example 2 Base Oil 1, wt. % 93.40 18.68 Base Oil 2,wt. % — 74.72 Additive Package, wt. % 6.60 6.60 Physical Properties ofLubricant SAE Viscosity Grade 40 20 Kinematic Viscosity, 100° C., mm²/s12.96 8.06 Sulfated Ash, wt. % 0.03 0.03 Test Results Deposit, wt. %24.42 14.37

Examples 3-4

Lubricating oil compositions 3 and 4 were formulated to meet dual fuelengine oil specifications and major dual fuel engine manufacturers'requirements. The results are presented in Table 5.

TABLE 5 Example 3 Example 4 Base Oil 1, wt. % 90.54 18.11 Base Oil 2,wt. % — 72.43 Additive Package, wt. % 9.46 9.46 Physical Properties ofLubricant SAE Viscosity Grade 40 20 Kinematic Viscosity, 100° C., mm²/s13.46 8.37 Sulfated Ash, wt. % 0.70 0.70 Test Results Deposit, wt. %14.37 12.39

Examples 5-6

Lubricating oil compositions 5 and 6 were formulated to meet low ashnatural engine oil specifications and major natural gas enginemanufacturers' requirements. The results are presented in Table 6.

TABLE 6 Example 5 Example 6 Base Oil 1, wt. % 91.8 18.36 Base Oil 2, wt.% — 73.44 Additive Package, wt. % 8.20 8.20 Physical Properties ofLubricant SAE Viscosity Grade 40 20 Kinematic Viscosity, 100° C., mm²/s13.64 8.61 Sulfated Ash, wt. % 0.45 0.45 Test Results Deposit, wt. %28.76 13.73

Examples 7-8

Lubricating oil compositions 7 and 8 were formulated to meet marineengine oil specifications and major marine engine manufacturers'requirements. The results are presented in Table 7.

TABLE 7 Example 7 Example 8 Base Oil 1, wt. % 88.60 17.72 Base Oil 2,wt. % — 70.88 Additive Package, wt. % 11.40 11.40 Physical Properties ofLubricant SAE Viscosity Grade 40 20 Kinematic Viscosity, 100° C., mm²/s13.40 8.55 Sulfated Ash, wt. % 3.10 3.10 Test Results Deposit, wt. %2.51 1.28

Examples 9-10

Lubricating oil compositions 9 and 10 were formulated to meet locomotiveengine oil requirements and major locomotive engine manufacturers'requirements. The results are listed in Table 8.

TABLE 8 Example 9 Example 10 Base Oil 1, wt. % 90.30 18.06 Base Oil 2,wt. % — 72.24 Additive Package, wt. % 9.70 9.70 Physical Properties ofLubricant SAE Viscosity Grade 40 20 Kinematic Viscosity, 100° C., mm²/s14.02 8.79 Sulfated Ash, wt. % 1.15 1.15 Test Results Deposit, wt. %24.7 9.62

Examples 1-10 show that lubricating oil compositions containing a heavybase stock in combination with a light base stock provided improveddeposit control over lubricating oil compositions containing solelyheavy base stock.

Examples 11-13

Lubricating oil compositions 11-13 were formulated to meet natural gasengine oil specifications and major natural gas engine manufacturers'requirements. The results are presented in Table 9.

TABLE 9 Example 11 Example 12 Example 13 Base Oil 1 wt. % 39.33 15.7388.67 Base Oil 2, wt. % 39.34 62.94 — Additive Package, wt. % 11.3311.33 11.33 2300 MW Polyisobutylene, 10 10 0 wt. % Physical Propertiesof Lubricant SAE Viscosity Grade 40 40 40 Kinematic Viscosity, 100° C.,15.98 13.61 13.56 mm²/s Sulfated Ash, wt. % 0.71 0.71 0.71 Test ResultsDeposit, wt. % 13.46 8.43 20.19

1. A natural gas engine lubricating oil composition comprising: (a) afirst base oil component selected from a Group I base stock, a Group IIbase stock, a Group III base stock, or a combination thereof, eachhaving a kinematic viscosity at 100° C. of from 8.5 to 15 mm²/s; and (b)a second base oil component selected from a Group I base stock, a GroupII base stock, a Group III base stock, or a combination thereof, eachhaving a kinematic viscosity at 100° C. of from 4.0 to less than 8.5mm²/s; wherein the weight ratio of the first base oil component to thesecond base oil component is in a range of from 1:10 to 1:1.15.
 2. Alow-speed or medium-speed diesel engine lubricating oil compositioncomprising: (a) a first base oil component selected from a Group I basestock, a Group II base stock, a Group III base stock, or a combinationthereof, each having a kinematic viscosity at 100° C. of from 8.5 to 15mm²/s; and (b) a second base oil component selected from a Group I basestock, a Group II base stock, a Group III base stock, or a combinationthereof, each having a kinematic viscosity at 100° C. of from 4.0 toless than 8.5 mm²/s; wherein the weight ratio of the first base oilcomponent to the second base oil component is in a range of from 1:10 to1:1.15.
 3. The lubricating oil composition of any one of claim 1 or 2,wherein the weight ratio of the first base oil component to the secondbase oil component is in a range of from 1:5 to 1:1.15.
 4. Thelubricating oil composition of any one of claim 1 or 2, which is a SAE20, SAE 30, SAE 40, SAE 50 or SAE 60 viscosity grade engine oil.
 5. Thelubricating oil composition of any one of claim 1 or 2, which is a15W-x, 20W-x or 25W-x SAE viscosity grade engine oil, wherein x is 30,40, 50 or
 60. 6. The lubricating oil composition of claim 2, wherein themedium-speed diesel engine lubricating oil composition is substantiallyzinc-free.
 7. The lubricating oil composition of claim 1, wherein thelubricating oil composition is used to lubricate a natural gas engineselected from a stationary natural gas engine, a stationary biogasengine, a stationary landfill gas engine, a stationary unconventionalnatural gas engine, or a dual-fuel engine.
 8. The lubricating oilcomposition of claim 2, wherein the lubricating oil composition is usedto lubricate a low-speed diesel engine and the low-speed diesel engineis a marine crosshead diesel engine.
 9. The lubricating oil compositionof claim 2, wherein the lubricating oil composition is used to lubricatea medium-speed diesel engine selected from a locomotive diesel engine, amarine trunk piston diesel engine or a land-based stationary powerdiesel engine.
 10. The lubricating oil composition of any one of claim 1or 2, further comprising 1 to 20 wt. %, based on the total weight of thecomposition, of a polyisobutylene having a kinematic viscosity at 100°C. of from 200 to 5000 mm²/s.
 11. The lubricating oil composition of anyone of claim 1 or 2, further comprising at least one additive selectedfrom an antioxidant, anti-wear agent, metal detergent, dispersant,friction modifier, corrosion inhibitor, demulsifier, viscosity modifier,pour point depressant, foam inhibitor, and mixtures thereof.
 12. Amethod of controlling deposit formation in a mechanical component of aninternal combustion engine selected from a natural gas engine, alow-speed diesel engine or a medium-speed diesel engine, the methodcomprising operating the internal combustion engine with a lubricatingoil composition comprising: (a) a first base oil component selected froma Group I base stock, a Group II base stock, a Group III base stock, ora combination thereof, each having a kinematic viscosity at 100° C. offrom 8.5 to 15 mm²/s; and (b) a second base oil component selected froma Group I base stock, a Group II base stock, a Group III base stock, ora combination thereof, each having a kinematic viscosity at 100° C. offrom 4.0 to less than 8.5 mm²/s; wherein the weight ratio of the firstbase oil component to the second base oil component is in a range offrom 1:10 to 1.1:15.
 13. The method of claim 12, wherein the mechanicalcomponent is a piston, a piston ring, a cylinder liner, a cylinder, acam, a tappet, a lifter, a gear, a valve, a valve guide, or a bearingincluding a journal, a roller, a tapered, a needle, or a ball bearing.14. The method of claim 12, wherein the mechanical component comprisessteel.
 15. The method of claim 12, wherein the internal combustionengine is operated under a load with a Brake Mean Effective Pressure ofgreater than 20 bar (2.0 MPa).